Active acoustic systems can be overwhelmed by false alarms due to reverberation and environmental features. The false alarms are particularly problematic during a search mode where target location is completely unknown. In a multi-static system, detections from each ping are monitored on multiple receivers and most of these are false alarms; actual target echoes may or may not be present. The multiplicity of false alarms leads to the formation of false target tracks that must be sorted out over time.
It is therefore desirable to have information that permits focusing on a target search region to reduce false alarms and enables more rapid winnowing of false target tracks. In addition, it is desirable to conserve the energy required for a full active search by choosing active sources in a favorable position relative to tracks originated from passive acoustic systems.